The present invention relates to live roller conveyors used to transport articles along a predetermined path and, more particularly, to zero pressure accumulation conveyors and trigger assemblies therefor.
Live roller conveyors and, even more particularly, accumulation conveyors, are well known in the art. Such accumulation conveyors have, in the past, employed various mechanisms for controlling the rotation of the conveyor rollers to allow them to be selectively rotated or stopped to accommodate accumulation of the articles being conveyed by the conveyors. The rollers are rotated to convey the articles to a collection or accumulation location and, once one or more of the articles have reached that location or locations, the rollers are stopped to provide for accumulation.
One such conveyor and control mechanism is shown in U.S. Pat. No. 3,696,912 (Fleischauer et al.). That patent discloses a live roller conveyor having a brake assembly which is mechanically actuated by a trigger assembly which senses the presence of the article at its desired accumulation location. The trigger assembly is mechanically coupled by a cable or chain to the brake assembly to cause the brake assembly to engage a key on a driven shaft which, in turn, drives the conveyor rollers to lock the driven shaft against rotation. The trigger assembly in that patent comprises a pivoted arm with a roller at the top which extends into the path of the articles and the roller is depressed by an article when the article arrives over the roller.
Although the trigger assembly disclosed in the aforementioned patent is quite suitable for use in the conveyance of almost all articles which are usually encountered in such uses, the trigger assembly disclosed therein has a disadvantage that at least one of the live rollers in each section in which the trigger assembly is located must be removed to accommodate the trigger assembly. This is disadvantageous where the articles being conveyed are short in length, i.e., short in the direction of the path in which the articles are being conveyed, or where the bottom surface of the article which rests upon the live rollers otherwise has poor traction qualities. When the articles are short or have poor traction, a situation may arise where sufficient traction is absent to restore movement to the article once it has been stopped due to loss of driving traction because of the removal of the live roller in order to accommodate the dead trigger roller. In such cases, it would be advantageous if the trigger assembly could be installed without the need to remove and lose any of the live rollers.
In U.S. Pat. No. 3,840,110 (Molt et al.), a trigger assembly is disclosed for a live roller accumulation conveyor which does not necessitate removal of any of the live rollers. However, the trigger assembly shown in that patent has the disadvantage that articles can be moved in only one direction on the conveyor because the trigger assembly interferes with movement of the articles in the opposite direction. In certain conveyor installations, dual directional movement of the articles may be desired, such as where the conveyor might be reversible or where it may be desirable at times to manually move the articles backward or upstream on the conveyor to clear a jam.
The zero pressure accumulation conveyor and trigger assembly of the present invention overcome the several aforementioned disadvantages of the prior constructions. A zero pressure accumulation conveyor and trigger assembly constructed in accordance with the principles of the present invention eliminate the need to remove any of the live rollers in the conveyor, thus assuring maximum tractional contact between the live rollers and the articles being conveyed at all times. In a zero pressure accumulation conveyor and trigger assembly incorporating the principles of the present invention, articles being conveyed may be readily moved in either direction on the conveyor without interference from the trigger assembly. A zero pressure accumulation conveyor and trigger assembly constructed in accordance with the principles of the present invention is safe, quiet and simple in construction, thereby substantially reducing the need for maintenance and in time in assembling of the conveyor, and the need for maintaining a substantial spare parts inventory is also reduced.
In one principal aspect of the present invention, a trigger assembly for sensing the presence or absence of articles on a conveyor of the kind having a plurality of rotatable rollers arranged in a plane and spaced from each other in the direction of the path of travel of the articles being conveyed to convey the articles is provided. The trigger assembly includes elongate cam means and mounting means for mounting the cam means to the conveyor for pivotal movement about an axis at or above the axes of rotation of the conveyor rollers. The cam means also includes first leg means spaced from the mounting means toward one end of the cam means and extending upwardly between a pair of the spaced conveyor rollers when the cam means is mounted by the mounting means on the conveyor. The upper end of the leg means is movable to a first upper position in which it extends above the plane of the conveyor rollers in the absence of an article, and a second lower position in which the upper end of the leg means is urged by an article moving in either direction on the conveyor so that it is substantially in the plane defined by the plane of the conveyor rollers. Sensing means is also included which is responsive to the movement of the leg means and the cam means about the mounting means for controlling the operation of the conveyor.
In still another principal aspect of the present invention, the aforementioned trigger assembly includes roller means rotatably mounted adjacent the upper end of the leg means and extending between the conveyor rollers. The roller means is rotatable about an axis which is substantially parallel to the axes of rotation of the conveyor rollers and that axis of rotation of the roller means remains below the plane of the conveyor rollers when the roller means is in its uppermost position.
In another principal aspect of the present invention, the aforementioned brake assemblies are employed in combination with a plurality of live rotatable conveyor rollers, drive means for rotating the conveyor rollers, and control means responsive to the trigger assembly to cause the drive means to rotate the conveyor rollers when the trigger assembly leg means is in its first position, and to cease rotating the conveyor rollers when the trigger assembly leg means is in its second position.
In still another principal aspect of the present invention, the aforementioned control means couples a plurality of the trigger assemblies and drive means to operate separate sections of the conveyor rollers in either a singulation mode or a slug mode.
These and other objects, features and advantages of the present invention will become apparent upon consideration of the detailed description of the invention to follow.